uniquekey constraint requires that every value in a column or set of columns beunique. No rows of a table may have duplicate values in a column (the uniquekey) or set of columns (the composite unique key) with a unique key constraint. Note: Because the database enforces a unique constra...
Because of the searchmechanism for unique key constraints on multiple columns, you cannot haveidentical values in the non-null columns of a partially null composite uniquekey constraint. 二. 相关测试 2.1 测试unique index 和 uniqueconstraint SYS@anqing2(rac2)> create table ut(idnumber,phone varchar...
Because of the searchmechanism for unique key constraints on multiple columns, you cannot haveidentical values in the non-null columns of a partially null composite uniquekey constraint. 二. 相关测试 2.1 测试unique index 和 uniqueconstraint SYS@anqing2(rac2)> create table ut(idnumber,phone varchar...
会注意到创建约束时有Primary Key、Check、Unique和Foreign Key四种类型的约束，这与SQL Server中的约束没...
AUniqueConstraintprohibits multiple rows from having the same value in the same column or combination of columns but allows some values to be null. The list of columns constrained by the UniqueConstraint is stored by column name. Nested Class Summary ...
Nonunique indexes permit duplicates values in the indexed column or columns. For example, the first_name column of the employees table may contain multiple Mike values. For a nonunique index, the rowid is included in the key in sorted order, so n...
select OWNER,CONSTRAINT_NAME ,COLUMN_NAME,POSITION from User_cons_columns where TABLE_NAME='EMP'; We will get null values for the Position column if we have a single column in the constraint. If there are multiple columns present in the constraints, Position will specify the order of the co...
CONSTRAINT[constraint_name]CHECK(condition); Checkconstraintscanbecreatedoraddedasatableconstraint, andwhenCheckconstraintsprotectmultipledatacolumns,table constraintsyntaxmustbeused.Theconstraintnameisoptional, andifthenamedoesnotexist,thenOraclewillproduceaunique ...
UniqueKeys PrimaryKeys ForeignKeys ForeignKeyColumns ProcedureParameters 資料行 ColumnNameDataType描述 OWNERString資料表、檢視表或叢集的擁有人。 TABLE_NAMEString資料表、檢視表或叢集名稱。 COLUMN_NAMEString資料行名稱。 識別碼Decimal所建立之資料行的序號。
The referenced unique or primary key constraint on the parent table or view must already be defined. 引用唯一或主键约束,必须是父表中已经定义的。 A composite foreign key cannot have more than 32 columns. 外键的组合列不能超过32列。 The child and parent tables must be on the same database. ...